Model Asus P2520L
MB P552LA_LJ Rev 2.1 with soldered I3 5010U processor
Boardview and repair guide found in the forum.
Received this laptop which could not power on.
Found +3VA_EC almost shorted (7ohm).
Tried removing U3001 EC controller IT8585E FXA: still shorted
tried removing PU9100 dual power switch which activates +3VA_EC :still shorted.
Found U3101 TPM Chip pin 1 shorted to ground : removed chip and shorted is gone. Replaced TPM chip with another taken from a similar board.
Replaced U3001 EC controller with a new IT8585E FXS
Replaced PU9100 with a new one.
Now +3VA_EC is present and power on sequence starts until VCCIN enable and reboots. Found that PU8000 VCCIN regulator has pin 6 CORE_PWRGD internally shorted to ground. Waiting for a replacement chip I cut the trace of CORE_PWRGD going to EC controller.
Now laptop starts to POST and BIOS is displayed. Installed Windows 10 and updated BIOS (main and EC) to last available version (207) using EZFLASH utility.
During installation found that occasionally some characters are displayed and windows are open and updated without pressing any key.
In Windows text editor most of the times the string "nbz" is displayed randomly. The problem is randomly present even in the BIOS where hour, minute and date changes by itself even disconnecting keyboard ribbon cable.
Checked the 24 connections from EC controller to keyboard connection both statically with ohmmeter for short or open circuit and dinamically with oscilloscope and everything looks ok. Tried a different keyboard : same problem. Touch pad works well. Sometimes keyboard works fine for minutes and then goes wild.
Replaced EC controller again with a new one : same problem. Reflashed BIOS with original one : same problem.
This stupid problem is driving me crazy and while logic would say that it's either a keyboard or EC controller fault, there must be something else.
I have 2 doubts :
1) EC controller version as original one is IT8585E FXA while new ones are IT8585E FXS : are they different in managing keyboard (I found out that this motherboard does not have filtering capacitor , nor pullup resistor on keyboard lines. Only has schottky diodes for ESD)
2) there are interferences or problems on the connection buses between EC controller and processor (SPI or most probably LPC Bus where also the TPM chip is connected)
Does anybody knows how EC controller sends keyboard data to Controller?
Any idea where the problem might be or what to check?
Thanks
MB P552LA_LJ Rev 2.1 with soldered I3 5010U processor
Boardview and repair guide found in the forum.
Received this laptop which could not power on.
Found +3VA_EC almost shorted (7ohm).
Tried removing U3001 EC controller IT8585E FXA: still shorted
tried removing PU9100 dual power switch which activates +3VA_EC :still shorted.
Found U3101 TPM Chip pin 1 shorted to ground : removed chip and shorted is gone. Replaced TPM chip with another taken from a similar board.
Replaced U3001 EC controller with a new IT8585E FXS
Replaced PU9100 with a new one.
Now +3VA_EC is present and power on sequence starts until VCCIN enable and reboots. Found that PU8000 VCCIN regulator has pin 6 CORE_PWRGD internally shorted to ground. Waiting for a replacement chip I cut the trace of CORE_PWRGD going to EC controller.
Now laptop starts to POST and BIOS is displayed. Installed Windows 10 and updated BIOS (main and EC) to last available version (207) using EZFLASH utility.
During installation found that occasionally some characters are displayed and windows are open and updated without pressing any key.
In Windows text editor most of the times the string "nbz" is displayed randomly. The problem is randomly present even in the BIOS where hour, minute and date changes by itself even disconnecting keyboard ribbon cable.
Checked the 24 connections from EC controller to keyboard connection both statically with ohmmeter for short or open circuit and dinamically with oscilloscope and everything looks ok. Tried a different keyboard : same problem. Touch pad works well. Sometimes keyboard works fine for minutes and then goes wild.
Replaced EC controller again with a new one : same problem. Reflashed BIOS with original one : same problem.
This stupid problem is driving me crazy and while logic would say that it's either a keyboard or EC controller fault, there must be something else.
I have 2 doubts :
1) EC controller version as original one is IT8585E FXA while new ones are IT8585E FXS : are they different in managing keyboard (I found out that this motherboard does not have filtering capacitor , nor pullup resistor on keyboard lines. Only has schottky diodes for ESD)
2) there are interferences or problems on the connection buses between EC controller and processor (SPI or most probably LPC Bus where also the TPM chip is connected)
Does anybody knows how EC controller sends keyboard data to Controller?
Any idea where the problem might be or what to check?
Thanks
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